Stationary and dynamic radial transverse electric polarizer for high numerical aperture systems

ABSTRACT

A radial transverse electric polarizer device includes a substrate material having a first refractive index and a plurality of elongated azimuthally oriented elements coupled to the substrate material, the plurality of elongated elements having a second refractive index. The plurality of elements are periodically spaced apart to form a plurality of gaps such that the radial transverse electric polarizer device interacts with an electromagnetic radiation including first and second polarizations to reflect substantially all of the radiation of the first polarization and transmit substantially all of the radiation of the second polarization. The plurality of elongated elements are coated with this thin layer of absorbing material which absorbs radiation at a wavelength of the electromagnetic radiation. The polarizer device may be used, for example, in a lithographic projection apparatus to increase imaging resolution.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/374,509, filed Feb. 27, 2003, now U.S. Pat. No. 6,943,941 the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical polarizers in general, and moreparticularly, to polarizers for high numerical aperture lithography.

2. Background of the Invention

A lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, a patterningdevice generates a circuit pattern corresponding to an individual layerof the IC, and this pattern can be imaged onto a target portion (e.g.comprising one or more dies) on a substrate (silicon wafer) that hasbeen coated with a layer of radiation sensitive material (resist). Ingeneral, a single wafer or substrate will contain a whole network ofadjacent target portions that are successively irradiated via theprojection system, one at a time.

The term “patterning device” as here employed should be broadlyinterpreted as referring to device that can be used to endow an incomingradiation beam with a patterned cross-section, corresponding to apattern that is to be created in a target portion of the substrate. Theterm “light valve” can also be used in this context. Generally, thepattern will correspond to a particular functional layer in a devicebeing created in the target portion, such as an integrated circuit orother device.

An example of such a patterning device is a mask. The concept of a maskis well known in lithography, and it includes mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. Placement of such a mask in the radiation beam causesselective transmission (in the case of a transmissive mask) orreflection (in the case of a reflective mask) of the radiation impingingon the mask, according to the pattern on the mask. In the case of amask, the support will generally be a mask table, which ensures that themask can be held at a desired position in the incoming radiation beam,and that it can be moved relative to the beam if so desired.

Another example of a patterning device is a programmable mirror array.One example of such an array is a matrix-addressable surface having aviscoelastic control layer and a reflective surface. The basic principlebehind such an apparatus is that, for example, addressed areas of thereflective surface reflect incident light as diffracted light, whereasunaddressed areas reflect incident light as undiffracted light. Using anappropriate filter, the undiffracted light can be filtered out of thereflected beam, leaving only the diffracted light behind. In thismanner, the beam becomes patterned according to the addressing patternof the matrix addressable surface.

An alternative embodiment of a programmable mirror array employs amatrix arrangement of tiny mirrors, each of which can be individuallytilted about an axis by applying a suitable localized electric field, orby employing piezoelectric actuators. Once again, the mirrors are matrixaddressable, such that addressed mirrors will reflect an incomingradiation beam in a different direction to unaddressed mirrors. In thismanner, the reflected beam is patterned according to the addressingpattern of the matrix-addressable mirrors. The required matrixaddressing can be performed using suitable electronics. In both of thesituations described hereabove, the patterning device can comprise oneor more programmable mirror arrays. More information on mirror arrays ashere referred to can be seen, for example, from U.S. Pat. Nos. 5,296,891and 5,523,193, and PCT publications WO 98/38597 and WO 98/33096. In thecase of a programmable mirror array, the support may be embodied as aframe or table, for example, which may be fixed or movable as required.

Another example of a patterning device is a programmable LCD array. Anexample of such a construction is given in U.S. Pat. No. 5,229,872. Asabove, the support in this case may be embodied as a frame or table, forexample, which may be fixed or movable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table. However, the general principles discussed in such instancesshould be seen in the broader context of the patterning device ashereabove set forth.

In current apparatus, employing patterning by a mask on a mask table, adistinction can be made between two different types of machine. In onetype of lithographic projection apparatus, each target portion isirradiated by exposing the entire mask pattern onto the target portionat once. Such an apparatus is commonly referred to as a wafer stepper.In an alternative apparatus, commonly referred to as a step and scanapparatus, each target portion is irradiated by progressively scanningthe mask pattern under the radiation beam in a given reference direction(the “scanning” direction) while synchronously scanning the substratetable parallel or anti-parallel to this direction. Since, in general,the projection system will have a magnification factor M (generally <1),the speed V at which the substrate table is scanned will be a factor Mtimes that at which the mask table is scanned. More information withregard to lithographic devices as here described can be seen, forexample, from U.S. Pat. No. 6,046,792.

In a known manufacturing process using a lithographic projectionapparatus, a pattern (e.g. in a mask) is imaged onto a substrate that isat least partially covered by a layer of radiation sensitive material(resist). Prior to this imaging, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake and measurementand/or inspection of the imaged features. This array of procedures isused as a basis to pattern an individual layer of a device, e.g. an IC.Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation, chemical,mechanical polishing, etc., all intended to finish off an individuallayer. If several layers are required, then the whole procedure, or avariant thereof, will have to be repeated for each new layer and theoverlay (juxtaposition) of the various stacked layers is performed asaccurate as possible. For this purpose, a small reference mark isprovided at one or more positions on the wafer, thus defining the originof a coordinate system on the wafer. Using optical and electronicdevices in combination with the substrate holder positioning device(referred to hereinafter as “alignment system”), this mark can then berelocated each time a new layer has to be juxtaposed on an existinglayer, and can be used as an alignment reference. Eventually, an arrayof devices will be present on the substrate (wafer). These devices arethen separated from one another by a technique such as dicing or sawing,whence the individual devices can be mounted on a carrier, connected topins, etc. Further information regarding such processes can be obtained,for example, from the book “Microchip Fabrication: A Practical Guide toSemiconductor Processing”, Third Edition, by Peter van Zant, McGraw HillPublishing Co., 1997, ISBN 0-07-067250-4.

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens.” However, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the beam of radiation, and such components may also bereferred to below, collectively or singularly, as a “lens.” Further, thelithographic apparatus may be of a type having two or more substratetables (and/or two or more mask tables). In such “multiple stage”devices the additional tables may be used in parallel or preparatorysteps may be carried out on one or more tables while one or more othertables are being used for exposures. Dual stage lithographic apparatusare described, for example, in U.S. Pat. Nos. 5,969,441 and 6,262,796.

Development of new tools and methods in lithography have lead toimprovements in resolution of the imaged features patterned on a device,e.g. an IC. Tools and techniques in optical lithography continue toimprove possibly leading to a resolution of less than 50 nm. This may beaccomplished using relatively high numerical aperture (NA) lenses(greater than 0.75 NA), wavelengths down to 157 nm, and a plethora oftechniques such as phase shift masks, non-conventional illumination andadvanced photoresist processes.

The success of manufacturing processes at these sub-wavelengthresolutions will rely on the ability to print low modulation images orthe ability to increase the image modulation to a level that will giveacceptable lithographic yield.

Typically, the industry has used the Rayleigh criterion to evaluate theresolution and depth of focus capability of a process. The resolutionand depth of focus (DOF) are given by the following equations:Resolution=k ₁(λ/NA),andDOF=k ₂(λ/NA ²),where λ is the wavelength of the illumination source and k₁ and k₂ areconstants for a specific lithographic process.

Therefore, for a specific wavelength, as resolution is increased throughthe use of higher-NA tools, the depth of focus can decrease. The loss inDOF with high NA is well known. However, the polarization targets forhigh NA partially coherent systems have not been examined. According tothe following equation:

${I\left( {r,Z_{0}} \right)} = \left. {\sum\limits_{i}{{\int\limits_{s}}_{\;}^{\;}{{\mathbb{d}\rho}\;{J\left( \rho_{0} \right)}}}} \middle| {{FT}\mspace{14mu}\left\{ {{O\left( {\rho - \rho_{0}} \right)}{P_{i}(\rho)}{F_{i}\left( {\rho,z} \right)}{H\left( {\rho,Z_{0}} \right)}} \right.} \right.$

where the image I, in a given film such as a photoresist, is a functionof position r and specific for a given focus position Z₀. This equationis valid for all NAs and the image is the summation over allpolarization states i. The integral is over the source distributiondefined by J. The Fourier term within brackets represents the electricfield distribution at the exit pupil. The four terms inside the bracketare, respectively, the object spectrum O of the reticle pattern, apolarization function P, a film function F and a pupil function H.

According to this equation, high NA imaging is intrinsically linked withthe polarization state and the thin film structure, where the electricfield coupling and the power absorbed by a photoresist film can bedrastically altered. The power absorbed due to incident plane waves on aphotoresist film are proportional to the exposure necessary to developthe film.

Studies by Donis G. Flagello et al. published under the title “OpticalLithography into the Millennium: Sensitivity to Aberrations, Vibrationsand Polarization,” in the 25th Annual International Symposium onMicrolithography, SPIE, Feb. 27–Mar. 3, 2002, Santa Clara, Calif., USA,have shown that two orthogonal polarization (Transverse Electricpolarization TE and Transverse Magnetic Polarization TM) divergeextensively at high NA, up to a 25% power change. An imaging systemwould contain a multitude of incident angles, reducing this effect.However, alternating phase shift masks (PSMs) require a small partialcoherence which restricts the total number of angles and thus couldproduce similar exposure changes.

Results have been obtained through simulation which show that a criticaldimension difference from a completely polarized state and theunpolarized state depends on the numerical aperture NA. Results havealso shown that dense lines with an alternating phase shift mask (PSM)is the most critical feature and this has been explained by the factthat the pupil configuration essentially produces 2-beam interference atthe wafer level and this case tends to maximize the effects ofpolarization. If, for example, a numerical aperture of 0.85 (relativelyhigh) is selected and one wanted to limit the systematic criticaldimension CD error to less than 3%, the residual polarization should belimited to 10%. The critical dimension CD is the smallest width of aline or the smallest space between two lines permitted in thefabrication of a device. The simulation results also indicate the levelof pupil filling and partial coherence can lessen the effects ofpolarization. This has been shown by the small polarization influence onthe features using conventional illumination.

Therefore, as more phase masks are used and imaging technology thatdemands small coherence levels is used, newer metrology technologies forthe lens may be required. For example, high NA polarization effects mayresult in extremely tight specifications on illumination polarizationfor lithography tools.

The advent of a resolution-enhancement technique (RET) called “liquidimmersion” promises extending 157 nm optical lithography to well below70 nm and possibly below 50 nm without changes in illumination sources(lasers) or mask technology. According to a Massachusetts Institute ofTechnology (MIT) article by M. Switkes et al. entitled “ImmersionLithography at 157 nm” published in J. Vac. Sci. Technology B 19(6),November/December 2001, liquid immersion technology could potentiallypush out the need for next-generation lithography (NGL) technologiessuch as extreme ultraviolet (EUV) and electron projection lithography(EPL). The liquid immersion technology involves using chemicals andresists to boost resolution. Immersion lithography can enhance theresolution of projection optical systems with numerical apertures up tothe refractive index of the immersion fluid. The numerical aperture NAis equal to the product of the index n of the medium and the sinus ofthe half angle θ of the cone of light converging to a point image at thewafer (NA=n sin θ). Thus, if NA is increased by increasing the index n,the resolution can be increased (see equation: Resolution=k₁(λ/NA)).However, as stated above, higher NA may result in extremely tightspecifications on illumination polarization for lithography tools.Therefore, polarization plays an increased role in immersionlithography.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a radial transverseelectric polarizer device including a substrate material having a firstrefractive index, and a plurality of elongated azimuthally orientedelements coupled to the substrate material and the elongated elementshaving a second refractive index. The plurality of elements areperiodically spaced apart to form a plurality of gaps such that theradial transverse electric polarizer device interacts with anelectromagnetic radiation having first and second polarizations toreflect substantially all of the radiation of the first polarization andtransmit substantially all of the radiation of the second polarization.The radial transverse electric polarizer also includes a thin layer ofabsorbing material. The plurality of elongated elements are coated withthe thin layer of absorbing material which absorbs at a wavelength ofthe electromagnetic radiation. The thin layer of absorbing material isselected such that a portion of reflected radiation of the firstpolarization that may have been transformed into a secondary radiationof a second polarization is substantially absorbed by the thin layer ofabsorbing material. In this way, the thin layer of absorbing materialcan substantially eliminate polarization flare in the transmittedradiation of the second polarization.

In an embodiment of the present invention the first polarization is atransverse magnetic polarization (TM) and the second polarization is atransverse electric (TE) polarization. The plurality of elongatedelements can be formed of, for example, aluminum, chrome, silver andgold. The substrate material can be, for example, quartz, silicon oxide,silicon nitride, gallium arsenide a dielectric material, andcombinations thereof.

Another aspect of the invention is to provide a polarizer deviceincluding a polarizing component and an absorber disposed on a backsideof the polarizing component. The polarizing component interacts with anelectromagnetic radiation comprising first and second polarizations toreflect substantially all radiation of the first polarization andtransmit substantially all radiation of the second polarization. Theabsorber includes a material absorbing at a wavelength of theelectromagnetic radiation. The material absorbs substantially allradiation of the second polarization. The polarizer can be used in areflective-type lithographic apparatus.

In one embodiment the polarizing component includes a plurality ofelongated azimuthally oriented elements. The plurality of elements areperiodically spaced apart to form a plurality of gaps. The plurality ofelongating elements may be, for example, electrically conductive at thewavelength of the electromagnetic radiation. In an exemplary embodiment,the first polarization is a transverse magnetic polarization and thesecond polarization is a transverse electric polarization.

In another embodiment, the polarizing component includes a plurality ofrings disposed concentrically and are periodically spaced. In anexemplary embodiment, the first polarization is a transverse electricpolarization and the second polarization is a transverse magneticpolarization.

According to another aspect of the invention a lithographic projectionapparatus is provided. The apparatus includes a radiation systemconfigured to provide a beam of radiation, a support configured tosupporting a patterning device, the patterning device configured topattern the radiation beam according to a desired pattern, a substratetable configured to hold a substrate, a projection system configured toproject the patterned beam onto a target portion of the substrate, and apolarizer device constructed and arranged to polarize the beam ofradiation in a transverse electric polarization direction. The polarizerdevice includes a plurality of elongated elements and a thin layer ofabsorbing material, the thin layer of absorbing material absorbingradiation at a wavelength of the electromagnetic radiation. Theplurality of elongated elements are coated with the thin layer ofabsorbing material.

A further aspect of the invention there is provided a devicemanufacturing method including projecting a patterned beam of radiationonto a target portion of a layer of radiation-sensitive material atleast partially covering a substrate; and polarizing the beam ofradiation in a transverse electric polarization. Still another aspect ofthe invention is to provide a device manufactured a device using theabove method.

Although specific reference may be made in this text to the use of theapparatus according to the invention in the manufacture of ICs, itshould be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid crystal display panels,thin film magnetic heads, etc. One will appreciate that, in the contextof such alternative applications, any use of the terms “reticle”,“wafer” or “die” in this text should be considered as being replaced bythe more general terms “mask”, “substrate” and “target portion”,respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) andEUV (extreme ultra-violet radiation, e.g. having a wavelength in therange 5–20 nm), as well as particle beams, such as ion beams or electronbeams.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the invention will become moreapparent and more readily appreciated from the following detaileddescription of the presently preferred exemplary embodiments of theinvention, taken in conjunction with the accompanying drawings, ofwhich:

FIG. 1 schematically depicts a lithographic projection apparatusaccording to an embodiment of the invention;

FIG. 2A is a schematic illustration of a radial polarizer according toan embodiment of the present invention;

FIG. 2B is an enlarged view of gratings at an area of polarizer depictedin FIG. 2A;

FIG. 3 is an enlarged lateral view of the radial polarizer according toanother embodiment of the present invention;

FIG. 4 is a vector diagram showing the preferential polarizationdirection and the output from a TE polarizer according to theembodiments shown in FIGS. 2A and 3;

FIG. 5 is a plot of the exposure latitude versus depth of focus for acomparative example 1;

FIG. 6 is a plot of the exposure latitude versus depth of focus for anexample 1 of the present invention;

FIG. 7 is a schematic illustration of a radial polarizer according to analternative embodiment of the present invention;

FIG. 8 shows schematically an embodiment of a lithographic systemutilizing the radial TE polarizer of the present invention;

FIG. 9A shows a schematic illustration of a transverse polarizer havinga polarizing component and an absorber according to another embodimentof the present invention;

FIG. 9B shows a schematic illustration of an embodiment of polarizingcomponent used in the polarizer of FIG. 9A;

FIG. 9C shows a schematic illustration of another embodiment of apolarizing component used in the polarizer of FIG. 9A;

FIG. 10 is flow-chart representing a device manufacturing methodaccording to the present invention; and

FIG. 11 is a schematic illustration of another embodiment of a polarizeraccording to the present invention.

DETAILED DESCRIPTION

Several techniques have been used to create polarized light. There arebasically four techniques for polarizing a natural beam of light, i.e.non-polarized light. One technique is based on birefringent or biaxialmaterials. A second technique is based on the use of dichroic materialssuch as “polaroid.” A third technique employs thin-film technology andit uses Brewster's effect. A fourth technique is based on wire grids orconductive gratings.

The use of birefringent materials to polarize light is known in theproduction of birefringent polarizers. Birefringent polarizers can bemade from many crystals and also certain stretched polymers.Birefringent materials are materials having a different optical index inone direction compared to another. The degree of difference in theoptical index between the two directions varies with the wavelength ofthe light. The difference in index is used to separate beams of onelinear polarization from another. Use of birefringent polarizers ischaracterized by inefficiency, wavelength dependent performance andrequires highly collimated light. For these reasons birefringentpolarizers are not commonly used in optical projection systems.

Dichroic polarizers are polarizers designed to absorb one polarizationand transmit the other one. Most commonly used dichroic polarizersconsist of a polymeric sheet stretched to orient its molecules andtreated with iodine and/or other materials or chemicals such that themolecules absorb polarization of one orientation. Streched polymerspolarizers absorb all the intensity of one polarization and at least 15%of the transmitted polarization. Stretched polymer polarizers degradewith time as the light induces chemicals changes in the polymericmaterial resulting in the material becoming yellow or brittle. Dichroicpolarizers are also sensitive to heat and other environmental changes.

In the last decade a polarizer device has been developed in whichstretched polymer sheets are made birefringent. These stretched sheetsreflect one polarization and pass the other. One problem with thispolarizer technique is its low extinction ratio of approximately 15.While useful for some applications, this extinction ratio is notadequate for imaging applications without a secondary polarizer. Thistype of polarizer also suffers from the environmental problems discussedabove.

Thin film polarizer technology uses Brewster's effect in which a lightbeam incident on a surface of a material such as glass, plastic or thelike, at Brewster's angle (near 45 degrees) is divided into twopolarized beams one transmitted and the other one reflected. Thin filmpolarizer technology however limits the angular range of the light beamincidence. The acceptance angular range is very narrowly limited to afew degrees in most devices. Thin film polarizer technology also suffersfrom the wavelength dependence because of the dependence of Brewster'sangle on the wavelength of the incident light.

For an image projection system where applications of a polarized lightbeam are sought, a brighter beam is always desirable. The brightness ofa polarized beam is determined by numerous factors, one of the factorsbeing the light source itself. Another factor for a system that employsa polarizer is the angle of acceptance. A polarizer with a narrow orlimited acceptance angle cannot gather as much light from a divergentsource as a system that employs a wide acceptance angle. A polarizerwith large acceptance angles allows flexibility in the design of aprojection optical system. This is because it is not necessary for thepolarizer to be positioned and oriented within a narrow range ofacceptance angles with respect to the light source.

Another desired characteristic for a polarizer is to effectivelyseparate one component of polarization from the other component. This iscalled the extinction ratio, which is the ratio of the amount of lightof the desired polarization component to the amount of light of theundesired polarization component. Other desired characteristics includefreedom of positioning the polarizer in an optical projection systemwithout diminishing the efficiency of the polarizer and/or introducingadditional restrictions on the system such as orientation of the beametc.

Another polarization technique utilizes a conductive grating or wiregrid. A wire grid polarizer is a planar assembly of evenly spacedparallel electrical conductors whose length is much larger than theirwidth and the spacing between the conductive elements is less than thewavelength of the highest frequency light component of the incidentlight beam. This technique has been successfully used for a number ofyears in the radio frequency domain and up to the infrared region of thespectrum. Waves with a polarization parallel to the conductors (Spolarization) are reflected while waves of orthogonal polarization (Ppolarization) are transmitted through the grid. The wire grid polarizeris used mainly in the field of radar, microwaves, and infrared.

The wire grid polarizer technique has not been used for shorterwavelengths except in few instances in the visible wavelengths range.For example, in U.S. Pat. No. 6,288,840 a wire grid polarizer for thevisible spectrum is disclosed. The wire grid polarizer is imbedded in amaterial such as glass and includes an array of parallel elongatedspaced-apart elements sandwiched between first and second layers of thematerial. The elongated elements form a plurality of gaps between theelements which provide a refractive index less than the refractive indexof the first layer. The array of elements is configured to interact withelectromagnetic waves in the visible spectrum to reflect most of thelight of a first polarization and transmit most of the light of a secondpolarization. The elements have a period less than 0.3 microns andwidths less than 0.15 microns.

Another instance where a wire grid polarizer is used for polarization inthe visible spectrum is described in U.S. Pat. No. 5,383,053. A wiregrid polarizer is used in a virtual image display to improve reflectionand transmission efficiency over conventional beam splitters. The wiregrid polarizer is used as a beam splitting element in an on-axis,polarized virtual image display. The extinction ratio of the gridpolarizer was not an issue in this application because the image wasalready polarized and only the relatively high efficiency of thereflection and transmission was of interest in this application.

Lopez et al., in an article published in Optics Letters, Vol. 23, No.20, pp. 1627–1629, describe the use of surface-relief gratingpolarization, similar to wire grid technology. Lopez et al. describe theuse of grating polarization in the visible spectrum (output of a He—Nelaser at 632.8 nm) as a quarter-wave plate polarizer (phase retardance,π/2) at normal incidence and as a polarizing beam splitter (PBS) at anangle of incidence of 40°. The polarizer is a one-dimensionalsurface-relief grating with a period of 0.3 microns and a 50% dutycycle. The grating material is a single layer of SiO₂ (index ofrefraction 1.457) sandwiched between two layers of Si₃N₄ (index ofrefraction 2.20) upon a fused-quartz substrate.

The wire grid polarizer technology has not been, however, suggested foruse in the ultraviolet wavelengths range, i.e. shorter than the visiblelower limit wavelength of 400 nm. As stated above, development of apolarizer for ultraviolet radiation would allow increases in resolutionof lithographic projection systems, and more specifically increases inthe resolution of lithographic projection systems having high NA, suchas in the case of immersion lithographic systems.

Ferstl et al., in an article published in SPIE Vol. 3879, September1999, pp. 138–146, discloses the use of “high-frequency” gratings aspolarization elements. Binary gratings with feature sizes smaller thanthe illumination wavelength of 650 nm were fabricated in quartz glass bymicrostructuring techniques using direct electron-beam writing combinedwith successive reactive ion etching. In polarization beam splittersdiffraction efficiencies of about 80% in the −1 order for transverseelectric TE polarization and 90% in the 0 order for transverse magneticTM polarization were obtained.

The polarization state of a wave can be defined by two parameters θ andφ, where θ defines the relative magnitudes of TE and TM wave components,and φ defines their relative phase. The incident wave can be expressedby the following pair of equations:A_(TE)=cos θ and A_(TM)=e^(jφ) sin θ

Thus, for φ=0, the wave is linearly polarized at an angle θ. Circularpolarization is obtained when θ=π/4 and φ=±π/2. A TE polarized wave isrepresented by θ=0. A TM wave is represented by θ=π/2. TE and TMpolarizations are fundamental polarization components.

Before going into details about polarization systems and polarizationlenses it would be judicious to put the polarization in the context ofits application, i.e. in the context of lithographic tools and methods.

FIG. 1 schematically depicts a lithographic projection apparatus 1according to an embodiment of the invention. The apparatus 1 includes aradiation system Ex, IL constructed and arranged to supply a beam PB ofradiation (e.g. EUV radiation), which in this particular case alsocomprises a radiation source LA; a first object table (mask table) MTprovided with a mask holder that holds a mask MA (e.g. a reticle), andconnected to a first positioning device PM that accurately positions themask with respect to a projection system PL. A second object table(substrate table) WT provided with a substrate holder that holds asubstrate W (e.g. a resist-coated silicon wafer), and connected to asecond positioning device PW that accurately positions the substratewith respect to the projection system PL. The projection system (“lens”)PL (e.g. a mirror group) is constructed and arranged to image anirradiated portion of the mask MA onto a target portion C (e.g.comprising one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (i.e. has atransmission mask). However, in general, it may also be of a reflectivetype, for example (with a reflective mask). Alternatively, the apparatusmay employ another kind of patterning device, such as a programmablemirror array of a type as referred to above.

The source LA (e.g. a discharge or laser-produced plasma source)produces radiation. This radiation is fed into an illumination system(illuminator) IL, either directly or after having traversed aconditioning device, such as a beam expander Ex, for example. Theilluminator IL may comprise an adjusting device AM that sets the outerand/or inner radial extent (commonly referred to as σ-outer and σ-inner,respectively) of the intensity distribution in the beam. In addition, itwill generally comprise various other components, such as an integratorIN and a condenser CO. In this way, the beam PB impinging on the mask MAhas a desired uniformity and intensity distribution in itscross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable directing mirrors). This latter scenario is oftenthe case when the source LA is an excimer laser. The present inventionencompasses both of these scenarios.

The beam PB subsequently intercepts the mask MA, which is held on a masktable MT. Having traversed the mask MA, the beam PB passes through thelens PL, which focuses the beam PB onto a target portion C of thesubstrate W. With the aid of the second positioning device PW andinterferometer IF, the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of the beamPB. Similarly, the first positioning device PM can be used to accuratelyposition the mask MA with respect to the path of the beam PB, e.g. aftermechanical retrieval of the mask MA from a mask library, or during ascan. In general, movement of the object tables MT, WT will be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which are not explicitlydepicted in FIG. 1. However, in the case of a wafer stepper (as opposedto a step and scan apparatus) the mask table MT may just be connected toa short stroke actuator, or may be fixed. The mask MA and the substrateW may be aligned using mask alignment marks M₁, M₂ and substratealignment marks P₁, P₂.

The depicted apparatus can be used in two different modes. In step mode,the mask table MT is kept essentially stationary, and an entire maskimage is projected at once, i.e. a single “flash,” onto a target portionC. The substrate table WT is then shifted in the X and/or Y directionsso that a different target portion C can be irradiated by the beam PB.

In scan mode, essentially the same scenario applies, except that a giventarget portion C is not exposed in a single “flash.” Instead, the masktable MT is movable in a given direction (the so-called “scandirection”, e.g., the Y direction) with a speed v, so that the beam PBis caused to scan over a mask image. Concurrently, the substrate tableWT is simultaneously moved in the same or opposite direction at a speedV =Mv, in which M is the magnification of the lens PL (typically, M=¼ or⅕). In this manner, a relatively large target portion C can be exposed,without having to compromise on resolution.

Currently, lenses that are used in projection lithography do not use TEpolarizers. They either have linear polarization or circularpolarization. The polarization state in the lithography tools used priorto the present invention are either linear, circular or unpolarized. Theinventors have determined that in order to improve resolution and allowbetter imaging under high NA, such as in immersion lithography where NAis greater than 1, it will require suppression of TM polarization forall feature orientations. Otherwise the loss of contrast would be severeenough to destroy any viable imaging.

In order to eliminate TM polarization and only use TE polarization inlithographic projection, the inventors have found that using radialpolarizers in circularly symmetric lenses allows for selectiveelimination of the TM polarization component. The manufacture of radialpolarizers is similar to that of wire grid technology describedpreviously. It is accomplished by the manufacture of radial periodicmetal lines such as, for example chrome or silver, dielectrics ormultilayers, either on a lens element or embedded within the lenselement.

FIG. 2A is a schematic illustration of an embodiment of a radialpolarizer according to the present invention. Radial polarizer 20 hasperiod gratings 22 arranged in a radially symmetric pattern. The periodof the grating can be selected for a specific wavelength of radiationused and in accordance with other desired parameters. In thisembodiment, the gratings are deposited on a substrate 24, which can beglass or other materials. The gratings 22 can be, for example, a metalsuch as aluminum, chrome, silver, gold or any material that isconductive at the wavelength the electromagnetic radiation beam. Thegratings can also be made, for example, of dielectrics or a combinationin a multilayer structure such as, but not limited to, a single layer ofSiO₂ sandwiched between two layers of Si₃N₄ on a fused-quartz substrate.The gratings 22 may also be etched using electron beams, for example,following a pattern transferred to a substrate of GaAs.

FIG. 2B is an enlarged view of gratings 22 at area 26 of polarizer 20.As shown in FIG. 2B gratings 22 are interlaced to allow smoothtransitions of the polarization effects to maintain uniformity of the TEpolarization intensity along the diameter of the polarizer.

Although the polarizer 22 is illustrated in FIG. 2A having a disk shape,the polarizer 20 can also be of a polygonal shape such as, but notlimited to, a rectangular shape, hexagonal shape, etc.

FIG. 3 is an enlarged lateral view of another embodiment of the radialpolarizer. Radial polarizer 30 includes a first layer of material 32having a first refractive index, a second layer of material 34 having asecond refractive index. A plurality of elongated elements 36 (orgratings) azimuthally and periodically spaced apart are disposed betweenthe first layer 32 and the second layer 34. The plurality of elongatedelements 36 interact with electromagnetic waves of light or radiation totransmit transverse electric TE polarization and reflect or absorb TMpolarization. The plurality of elongated elements 36 can be made, forexample, of silicon dioxide and the first and/or second layers 32 and/or34 can be made of any material comprising, for example, quartz,silicone, dioxide, silicon nitride, gallium arsenide etc. or adielectric material at the wavelength of the electromagnetic beam ofradiation. Similarly to the previous embodiment the spacing or periodbetween the elongated elements 36 can be selected according to theintended use of the polarizer, i.e. for a specific wavelength and inaccordance with other parameters in the lithographic system.

Similarly, although the polarizer 30 is illustrated in FIG. 3 as beingpart of or having a disk shape, the polarizer 30 can also be part of orhaving a polygonal shape such as, but not limited to, a rectangularshape, hexagonal shape, etc.

Light impinging on polarizer 20, 30 at near normal incidence would haveits polarization state altered such that the output of transmittedpolarization state is orthogonal to the direction of the grating lines22, 36 in the polarizer 20, 30.

FIG. 4 is a vector diagram 40 with the preferential polarizationdirection 41 and output from TE polarizer 20. Higher errors and defectswould be allowed towards the center of the polarizer as the need for TEpolarization with high NA systems is greater at the edge of the pupil. Acoherent light illuminating through dense lines (reticle image lines)will produce 3 orders of diffraction. At 42 would be the position of the0 order diffraction of the beam of light and at 44 and 45, therespective positions of the +1 order diffraction and −1 orderdiffraction, for a vertical line. At 46 and 47, the respective positionsof +1 order diffraction and −1 order of diffraction, for a horizontalline. The +1 and −1 order will interfere giving rise to valleys andpeaks in the illumination reaching the wafer. If a TE polarization isused, for both vertical and horizontal lines, an interference patternoccurs leading to a high contrast and thus to a good resolution of thelines.

Whereas, in the case of linear polarization only one of the vertical orhorizontal lines would lead to a clear interference pattern with highcontrast. The other vertical or horizontal line would not be correctlypolarized, not form an interference pattern and thus the contrast wouldbe less. The combination of high and low contrast images would averageout the result leading to a low definition or resolution imaging for theoverall pattern. To get rid of the component leading to absence or minorinterference at the wafer the inventors used a radial TE polarizer thatallows interference patterns to occur in any azimuthal direction in thelens. This would not be the case with circular polarization as eachcomponent is a combination of two linear orthogonal polarizations butcan be thought of as turning in space but in a fixed manner as functionof position. Therefore, the use of circular polarization would not leadto interference lines and consequently is not suitable for highresolution imaging for lithographic systems because in the wafer planecircular polarization is reduced to linear polarization and thedrawbacks of this were described above in this paragraph.

In an immersion lithographic system, i.e. a lithographic system with ahigh NA, the use of a TE polarizer may be required in order to obtainthe resolution adequate for imaging dense lines. FIG. 5 shows theprocess window for a comparative Example 1 unpolarized immersionlithographic system imaging 50 nm dense lines. The wavelength of use inthis example is 193 nm. The immersion fluid used is water with arefractive index of 1.437 (NA=1.437). The air equivalent numericalaperture NA is 1.29. The resist used in this example is PAR710 made bySumitomo Corp., Japan, on a matched substrate. The illumination isannular with σ=0.9/0.7. FIG. 5 is a plot of the exposure latitude versusdepth of focus for comparative Example 1. This plot indicates that theexposure latitude at a depth of focus of 0.0 is approximately 5.6%,which is an unusable level. At other depth of focus the exposurelatitude decreases even more which makes an unpolarized light unusablein lithographic system at high NA.

FIG. 6 shows the process window for a 50 nm dense lines with TEpolarized light and immersion optics according to an Example 1 of thepresent invention. The wavelength of use in this example is 193 nm. Theimmersion fluid used is water with a refractive index of 1.437(NA=1.437). The resist used, in this example, is Par710 on a matchedsubstrate. The illumination is annular with σ=0.9/0.7. FIG. 6 is a plotof the exposure latitude amount versus depth of focus. This plotindicates that the exposure latitude at a depth of focus of 0.0 isapproximately 9.9%, which is a usable level. An improvement in exposurelatitude of 75% is obtained when using TE radial polarization system ofExample 1 of the present invention compared to comparative Example 1. Animprovement in DOF of 27% is obtained in Example 1 of the presentinvention compared to comparative Example 1. Thus an increased processedwindow is enabled by the use of the TE polarizer of the presentinvention. At other depth of focus the exposure latitude decreases withthe increase of the depth of focus.

FIG. 7 is a schematic illustration of another embodiment of a radialpolarizer according to the present invention. Radial TE polarizer 70 iscomprised of a plurality of plate polarizers. Radial polarizer 70 isfabricated by cutting the plate polarizer 72 that have linearpolarization preference. The plate polarizers are cut into plate sectors72 a–h in order to fabricate a circular-shaped piece polarizer. Theplate sectors 72 a–h are then assembled to form a radial polarizer 70.Each plate sector 72 a–h has a linear polarization vector state 74 a–hand thus by assembling the plate sectors 72 a–h in this fashion thelinear vector polarization 74 a–h would rotate to form radialpolarization configuration. However, since the plate sectors arediscrete elements, in order to obtain a “continuous” TE radialpolarization, polarizer 70 is preferably rotated to randomize opticalpath differences between the plates and to insure uniformity. Therotation of the polarizer is not necessary but in some cases it wouldadd uniformity and depending on how the rotation is implemented, thespeed of the rotation could be selected to be very slow or very fast. Toperform such rotation the polarizer 70 can be mounted for example on airbearings. In the case of EUV lithography where at least parts of thelithographic system are in vacuum, an alternative mount solution can beprovided. For example, the polarizer 70 can be mounted on magneticbearing systems instead of air bearings. The speed of rotation wouldgovern the uniformity of the polarization. In general, the rotation rateshould be sufficiently high to randomize optical path differencesbetween the plates in order to insure uniformity.

FIG. 8 shows schematically an embodiment of a lithographic systemutilizing a radial TE polarizer of the present invention. As describedpreviously, lithographic system 80 comprises illumination or radiationsystem source 81, mask or reticle 82, projection lens 83, substrate orwafer 84 and a radial TE polarizer 20, 30, or 70. The radial TEpolarizer 20, 30, or 70 is shown in this embodiment positioned at theentrance of the projection lens, optimally close to the pupil plane,however, one ordinary skill in the art would appreciate that the radialpolarizer 20, 30, or 70 can be positioned anywhere in the projectionlens or outside the projection lens such as, for example, between thereticle or mask 82 and the projection lens 83.

A best performance for radial polarizer is achieved when the polarizeris an ideal polarizer having perfectly conducting gratings (for example,wire grids or elongated elements). In this situation, the radialpolarizer will function as a perfect mirror totally reflecting light ofone polarization (e.g., TM polarization) and will be perfectlytransparent for the light with the other polarization (e.g., TEpolarization). The desired polarization (TE polarization) will betransmitted while the undesired polarization (TM polarization) will bereflected.

However, if the radial polarizer is placed between the reticle 82 andthe projection lens 83, for example, the reflected light with theundesired polarization (TM polarization) may travel back to the reticle82. The reflected light with the undesired polarization may impinge onthe reticle 82 and be reflected back toward the radial polarizer. Inthis process, a portion of the light reflected by the reticle mayundergo a polarization change. If, for example, the polarization of thelight reflected by the reticle 82 has at least a portion of lightchanged into TE polarization (the desired polarization), this portion oflight with TE polarization (secondary light), can be transmitted by theradial polarizer since the radial polarizer is constructed to permitlight with TE polarization to pass through. This portion of TE polarizedlight, albeit less intense than the light with TE polarization that wasinitially transmitted through the radial polarizer (primary TEpolarization light), can pass through the radial polarizer and mayeventually reach the substrate 84. This reflection phenomenon may repeatitself numerous times resulting in a change of polarization in a pathback and forth to the radial polarizer. This may lead to the creation ofa flare in the polarization because secondary TE polarized light isadded to the TE polarized light that initially traversed the radialpolarizer (primary TE polarized light). The polarization flare canultimately lead to a blurr in the imaging and thus a loss in imagingresolution.

In order to minimize the possibility of occurrence of a polarizationflare in the imaging, the inventors have determined that coating theconducting gratings (e.g., wire grids) in the radial polarizer with athin absorber layer can help reduce back reflections from the polarizer,and from other objects in the lithographic apparatus, for example, thereticle 82.

In one embodiment, a thin absorber layer is optionally coated ongratings 22 of the radial polarizer 20 illustrated in FIG. 2A. Thegratings 22 can be conducting elements made from, for example, aluminum,chrome, silver, gold or a combination therefrom. The thin absorber layercan be, for example, any material that is absorbing at the wavelength ofradiation used, for example, Al₂O₃ and anodic oxidized aluminum. Thethin absorber layer may also contain a compound with low reflection. Asuitable compound with low reflection can be BILATAL made by a processfrom Zeiss, Germany. Other suitable low reflection compounds include AlNand CrO_(x) (x being an integer number).

By coating the gratings 22 of polarizer with a thin absorber layer, backreflections (secondary TE polarization) from the radial polarizer andfrom the reticle, are absorbed by the thin layer while the primary TEpolarized light is minimally absorbed by the thin absorber layer. Thisis because the light of the back reflections (secondary TE polarizedlight), being less intense than the primary TE polarized light, isrelatively easily absorbed by the thin absorber layer. The thickness andor the material of the absorber layer can be selected or adjusted toachieve a desired extinction of the back reflections secondary TEpolarized light.

In the above exemplary embodiment, it has been referred to absorbingback reflections occurring between the radial polarizer and the reticle,however, it should be appreciate that the above also applies in the caseof back reflections that may occur between any object in the path of thereflected polarization and the radial polarizer.

The above process for eliminating undesired polarization by using anabsorbing medium in conjunction with a radial polarizer is useful inimaging applications using a transmissive lithographic tool, an exampleof which is illustrated in FIG. 1. In the case of a reflectivelithographic tool, however, another configuration is used to eliminateundesired polarization. In reflective lithography, it is the reflectedpolarization that is used for imaging. Therefore, it is the transmittedundesired polarization that would be absorbed or eliminated.

FIG. 9A shows a schematic illustration of a polarizer with an absorberaccording to one embodiment of the invention. Polarizer 90 includes apolarizing component 92 and an absorber 94. Absorber 94 is disposed onthe back side of polarizing component 92 relative to incident light 96.Absorber 94 can be disposed directly in contact with a back surface ofpolarizing component 92 or slightly spaced apart from polarizer element92. Absorber 94 includes a material that absorbs at the wavelength ofradiation used, i.e. at the wavelength of incident light 96. Incidentlight 96 contains both TE component polarization and TM componentpolarization.

As stated previously, in reflective lithography, the reflectedpolarization is used for imaging while the transmitted polarization istransmitted. In this case, the TE polarization component 97 (desiredpolarization), for example, is reflected by polarizing component 92while the TM polarization component 98 (undesired polarization), forexample, is transmitted by polarizing component 92.

The transmitted TM polarization may encounter in its path an object,such as other optical imaging elements in the lithographic apparatus.Hence, a portion of the TM polarized light can be reflected back towardthe polarizing component 92. This portion of TM polarized light willtraverse the polarizing component 92 because the polarizing component 92is “transparent” to TM polarization. This portion of TM polarized light,albeit less intense than TE polarization light (desired polarization),can be added to and mixed with the desired TE polarization leading to adeterioration in the imaging resolution.

In order to eliminate possible back reflections from other opticalelements in the lithographic tool, the absorber 94 is introduced in thelight path of the undesired TM polarized light 98. In this way, the TMpolarized light is absorbed by absorber 94 along the thickness ta ofabsorber 94 and does not reach an object in the lithographic apparatusthat may reflect the TM polarization. In addition, even if the TMpolarized light is not totally eliminated in a first passage of thelight through thickness ta of absorber 94, the remaining TM polarizedlight 99 that may be reflected at the bottom surface 94B of absorber 94may be absorbed in its second passage through thickness ta of absorber94. Hence, the undesired TM polarization is absorbed twice by theabsorber 94 leading to a quadratic absorption/extinction of the TMpolarization component. This allows enhanced extinction of the TMpolarization component. The thickness ta and/or the material of theabsorber can be selected or adjusted to achieve a desired extinction ofthe back reflections secondary TE polarized light.

In an alternative embodiment, the polarizing component 92 may bedisposed on top of a transmitting substrate instead of the absorber 94.When the polarizing component 92 is disposed on top of a transmittingsubstrate, a quarter wave plate is disposed on the back of the substrateto absorb the undesired TM polarization. In either embodiments, theextinction of the TM polarization component is achieved by theincorporation of an absorber, be it an absorbing material or a quarterwave plate. Furthermore, a quarter wave plate may also be disposedbetween the polarizing component 92 and the absorber 94. In thisinstance, undesired TM polarization encounters the quarter wave plateand by passing the quarter wave plate becomes circularly polarized. Mostof this circularly polarized light will be absorbed by absorber 94.However, if there some light is reflected back by a surface of theabsorber 94. This reflected light will be sent towards the quarter waveplate and be polarized again circularly and thus changed into TEpolarization. Since the polarizing component 92 reflects TEpolarization, the light passing through the quarter wave plate a secondtime would be reflected by the polarizing component 92 and sent towardsthe absorber 94. In this way, this reflected light will be absorbed asecond time by the absorber 94. This provides an enhanced elimination orextinction of the undesired polarization component, i.e., TMpolarization.

The polarizing component 92 shown in FIG. 9A can have a structure of agratings polarizer 92A as illustrated schematically in FIG. 9B or astructure of a ring polarizer 92B as illustrated schematically in FIG.9C. The gratings polarizer 92A may be similar to the radial polarizer 20shown in FIG. 2A. The gratings polarizer 92A has period gratings 93arranged in a radially symmetric pattern azimuthally spaced apart. Thesolid arrows in FIG. 9B show the configuration/orientation of the TEpolarization component and dotted arrows show theconfiguration/orientation of the TM polarization component. As statedpreviously, the component polarization that has an orientationperpendicular to the gratings (grid-lines or elongated elements) aretransmitted while the polarization component parallel to the grid-linesis reflected. Thus, the gratings polarizer 92A is such that the TMpolarization is reflected and the TE polarization is transmitted. The TEpolarization is eventually absorbed by absorber 94 (shown in FIG. 9A).In this instance, the component used for imaging is the TM polarizationcomponent. This configuration of the absorbing element 92 is, however,rarely used in reflective lithography.

In contrast, the configuration shown in FIG. 9C of a ring polarizer 92Bis the most used in reflective lithography. The ring polarizer 92B hasrings 95 which can be disposed on absorber 94 (shown in FIG. 9A) ordisposed on a transmitting substrate as discussed above. The rings 95are disposed concentrically and are periodically spaced. The solidarrows in FIG. 9C show the configuration/orientation of the TEpolarization component and the dotted arrows show theconfiguration/orientation of the TM polarization component. As statedpreviously, the component polarization that has an orientationperpendicular to the gratings, i.e. perpendicular to a tangent of therings, are transmitted while the polarization component tangential tothe rings is reflected. In this case the TM polarization is transmittedwhile the TE polarization is reflected. The TM polarization iseventually absorbed by absorber 94 (shown in FIG. 9A). In this instance,the component used for imaging is the TE polarization component.

Referring to FIG. 10, a device manufacturing method according to thepresent invention includes providing a substrate that is at leastpartially covered by a layer of radiation-sensitive material S110,providing a beam of radiation using a radiation system S120, using apatterning device to endow the beam with a pattern in its cross-sectionS130, projecting the patterned beam of radiation onto a target portionof the layer of radiation-sensitive material S140, and polarizing thebeam of radiation in a transverse electric polarization S150.

FIG. 11 is a schematic illustration of another embodiment of a polarizer100 according to the present invention used to create tangentialpolarization. Conventional polarization systems are known to usepolarization units such as beam-splitting cubes. Beam-splitting cubesconsist of a pair of fused silica precision right-angle prisms carefullycemented together to minimize wave front distortion. The hypotenuse ofone of the prisms is coated with a multilayer polarizing beam-splittercoating (such as a birefringent material) optimized for a specificwavelength. The beam-splitter throws away an amount of incident light,and at the exit from the cube, in one of the two branches, the light islinearly polarized. Conventionally, in order to prevent differences inprinting horizontal and vertical lines, the polarization is renderedcircular with a quarter wave plate, in the pupil of the imaging system.

However as stated previously, circular polarization is comprised of bothfundamental polarization components TE and TM. In accordance with thepresent invention, a polarizer plate 102 is introduced in the pupil ofthe imaging system comprising the cube beam-splitter 103. In oneembodiment, the plate polarizer 102 comprises two half-wave plates 104Aand 104B. The plate polarizer 102 polarizes the linear polarized lightinto a first s-polarized light S1 and a second s-polarized light S2 suchthat a wave vector S1 of the first s-polarized light and a wave vectorS2 of the second polarized light are perpendicular to each other. Theplate polarizer is disposed at the end of the cube-beam-splitter 103such that one polarization direction is limited to only two quarters ofthe pupil. This is suitable for printing horizontal lines since thepolarization arrives as s-polarization on the wafer. In the other twoquarters segments, a half-wave phase shift is introduced throughbirefringence (under 45 degrees). The polarization that was sagital willrotate over 90 degrees and becomes also tangential. This, in turn, issuitable for printing vertical lines. In other words, the firsts-polarized light S1 is used to print lines on a wafer in a horizontaldirection and the second s-polarized light S2 is used to print lines ona wafer in a vertical direction. In this way, S-polarization or TEpolarization is obtained for both vertical and horizontal lines.

Furthermore, since numerous modifications and changes will readily occurto those of skill in the art, it is not desired to limit the inventionto the exact construction and operation described herein. Moreover, theprocess, method and apparatus of the present invention, like relatedapparatus and processes used in the lithographic arts tend to be complexin nature and are often best practiced by empirically determining theappropriate values of the operating parameters or by conducting computersimulations to arrive at a best design for a given application.Accordingly, all suitable modifications and equivalents should beconsidered as falling within the spirit and scope of the invention.

1. A lithographic projection apparatus, comprising: a radiation systemconfigured to provide a projection beam of radiation; a supportconfigured to support a patterning device, the patterning deviceconfigured to pattern the beam according to a desired pattern; asubstrate table configured to hold a substrate; a projection systemconfigured to project the patterned beam onto a target portion of thesubstrate; and a polarizer device constructed and arranged to polarizesaid beam of radiation in a transverse electric polarization direction,said polarizer device comprising a plurality of elongated elements and athin layer of absorbing material, said thin layer of absorbing materialabsorbing radiation at a wavelength of said beam of radiation, whereinsaid plurality of elongated elements are coated with said thin layer ofabsorbing material.
 2. A lithographic projection apparatus according toclaim 1, wherein said polarizer device further comprises: a first layerof material having a first refractive index; a second layer of materialhaving a second refractive index; and said plurality of elongatedelements are azimuthally and periodically spaced apart, and disposedbetween said first layer and said second layer, said plurality ofelongated elements interact with said beam of radiation to transmittransverse electric polarization of said beam of radiation.
 3. Alithographic projection apparatus according to claim 1, wherein saidpolarizer device further comprises: a substrate material having a firstindex; and said plurality of elongated elements are azimuthally orientedand coupled with said substrate material, said elongated elements havinga second refractive index, said plurality of elongated elements areperiodically spaced apart to form a plurality of gaps such that saidpolarizer device interacts with the beam of radiation comprising firstand second polarizations to reflect substantially all of the radiationof the first polarization and transmit substantially all of theradiation of the second polarization.
 4. A lithographic projectionapparatus according to claim 3, wherein said thin layer of absorbingmaterial is selected such that a portion of reflected radiation of thefirst polarization transformed into a secondary radiation of a secondpolarization is substantially absorbed by said thin layer of absorbingmaterial.
 5. A lithographic projection apparatus according to claim 3,wherein the radiation of the second polarization is minimally absorbedby said thin layer of absorbing material.
 6. A lithographic projectionapparatus according to claim 3, wherein said thin layer of absorbingmaterial substantially eliminates polarization flare in the transmittedradiation of a second polarization.
 7. A lithographic projectionapparatus according to claim 3, wherein the second polarization is atransverse electric polarization.
 8. A lithographic projection apparatusaccording to claim 1, wherein said thin layer of absorbing material isselected from the group: Al₂O₃ and anodic oxidized aluminum.
 9. Alithographic projection apparatus according to claim 1, wherein awavelength range of said radiation beam is in the ultraviolet spectrum.10. A lithographic projection apparatus according to claim 9, whereinsaid wavelength range is between 365 nm and 126 nm.
 11. A lithographicprojection apparatus according to claim 9, wherein said wavelength rangeis in the extreme ultraviolet.